The Science: The drink's most touted ingredient is L-theanine, an amino acid found in green tea leaves; it may help you calm down by increasing the brain's production of alpha waves, which are associated with relaxation. One small study found that people who took 50 milligrams of L-theanine (one can of Just Chill contains more than three times that amount) exhibited increased alpha activity.
Real-Life Road Test: "I'd reach for a can at 3 P.M., when my occasional state of unfocused frazzledness sets in. I was expecting to feel sleepy, but instead my productivity spiked, and I felt far more attuned to the task at hand. While I was pleasantly surprised by the 40 minutes of sharp concentration that followed, the aftertaste leaves something to be desired."
—Katie Arnold-Ratliff, Senior Editor